The swivel ones usually have a lever that activates the gas that allows it to go up and down. The gas mechanism is usually within the middle pole. That way you can adjust the height. I have seen some that adjust the height by swivelling round, swivel one way the seat goes up and swivel the other way it goes down.

IKEA Nilsolle

That height should work fine. If you are UK based, can I also suggest you look to atlanticshopping.co.uk for your bar stools? They specialise in them and have a huge range at very keen prices. There is a showroom (Birmingham direction, I think) if you want to see the product. We use them ourselves for the showroom, and many of our customers have used them and been very pleased with quality & value. If you are buying online, you should still have consumer rights which allow you to return product (just the postage cost lost at most) as long as the product is not "made to order" - in which case make sure you are sure before you buy!

Google says potterbarn.com do, but not here in the UK. Houzz shop is just links to other stores.